2016 NFPA Conference & Expo Rooftop Photovoltaic (PV) Systems Examining the Risks and Researching the Options Presented by: Joel Sipe Senior Managing Engineer Exponent Inc.
Outline Project Background Fire Incidents Fire Testing of Roofs and PV Modules Proposed Test Plan Mitigation Solutions to be Tested
Introduction Typical Rooftop PV Arrays Images from - http://blog.solarwaale.com/2016/01/04/additional-5000-crore-for-solar-rooftop-in-india/ (left) http://www.solarfeeds.com/barriers-rooftop-solar/ (right)
Introduction PV installations have recently become much more prevalent in the US due largely to reduced installation cost. Reduced installation cost is driven by many factors, including: Lower manufacturing cost. Federal and state government incentives. More efficient installation practices. Rapid expansion of use has created some technical and fire service challenges. Building codes and fire service tactics are evolving.
Introduction Current project is developing a test plan to evaluate mitigation solutions for fires involving rooftop PV arrays. Project is funded by the NFPA Fire Protection Research Foundation (FPRF). Guidance is provided by a technical panel with members from relevant industry sectors and the NFPA Property Insurance Research Group (PIRG).
Introduction Dietz and Watson fire, Delanco NJ, September 2013. Images from http://nj1015.com/fire-still-burns-at-south-jersey-warehouse-video/
The Challenge of Rooftop Fires & PV Arrays PV arrays add fuel and potential ignition sources to roofs. Fires that develop are outside the reach of the building fire detection and suppression systems. Presence of PV modules affects fire dynamics and can lead to fast growing fires. FDs cautious about going onto roofs with PV array fires. PROJECT GOAL: Mitigate flame spread to give FD more time to implement extinguishment plan.
PV Array Components Cells produce ~ 0.5V Modules produce ~25-50V National Electrical Code (NEC) limits system voltage - 600V for residential - 1000V or greater for commercial
Potential PV Failure Modes Cables Cells Junction Boxes Inverters Heating at cable connections Ground faults Poor bus bar contact to cells Cell cracking or thin metal cells leading to resistive heating Arcing or resistive heating at mechanical or solder contacts Diode failures Electronic component failure or shorting Trace melting leading to arc flash
Outline Project Background Fire Incidents Fire Testing of Roofs and PV Modules Proposed Test Plan Mitigation Solutions to be Tested
Fires Associated with PV Arrays April 2009: Bakersfield, CA Fire at a Target big-box retail store 383 kw array on roof, 166 strings of 11 modules, 1826 modules Fire reportedly started in 2 locations Fire cause reportedly ground fault related April 2011: Mount Holly, NC Fire at National Gypsum Co., a drywall manufacturing facility Fire cause reportedly ground fault related
Fires Associated with PV Arrays May 2013: LaFarge, WI Green building with metal roof Roof reportedly became energized and inhibited suppression activity
Fires Associated with PV Arrays September 2013: Delanco, NJ (shown) Dietz and Watson warehouse Building was ~300k sq ft Over 7,000 solar modules on roof PV system reportedly inhibited fire suppression activity November 2013: Florence Twp, NJ Fire at a 700k sq ft Christmas goods warehouse Over 8,000 modules on roof, 300 modules involved in the fire
Outline Project Background Fire Incidents Fire Testing of Roofs and PV Modules Proposed Test Plan Mitigation Solutions to be Tested
Fire Testing of Roofs and Modules Roofs Tested per ASTM E108 - Class A, B, or C rating PV Modules Tested per UL 1703 - Class A, B, or C rating Pre-2013 Tested without roof Post-2013 Tested as a system (module, roof, rack)
ASTM E108 Four fire tests: Intermittent flame exposure Spread of flame Burning brands Flying brands Roof assembly is given a Class A, B, or C rating
ASTM E108 - Spread of Flame Test Wind Roof Burner Wind
ASTM E108 Spread of Flame Gas burner 2-inch OD steel pipe with ½-inch by 36-inch slot Fire size Class A & B ~22,000 BTU/min (~387 kw) Class C ~19,000 BTU/min (~334 kw) Air flow 12 ± 0.5 mph (5.3 ± 0.2 m/s)
UL 1703 Pre-2013 Two fire tests: Spread of flame Burning brand Module is given a Class A, B, or C rating https://www.dewa.gov.ae/images/smartinitiatives/pv_on_buildings.pdf
UL 1703 2013 and later Five fire tests: Spread of flame on top surface of module Burning brand on surface of module over steep sloped roof Spread of flame between module and steep sloped roof Spread of flame between module and low sloped roof Burning brand between module and steep sloped roof Module is given a Class A, B, or C rating
Development of UL 1703-2013 Fire testing performed with PV modules on sloped roofs: Zero setback 5-inch standoff height (worst case scenario) Roof Rating PV Module Rating Flame Spread A C > 8 ft A A > 8 ft C C > 8 ft Non-combustible C > 8 ft Non-combustible A > 8 ft
Development of UL 1703-2013 Mitigation solutions were tested at UL: Vertical flashing With gap Not successful Without gap - Successful Fire barriers Some success Setback Not successful Screens Not successful
Gaps in Available Test Data/Knowledge Large-scale roof array fire tests. Mitigation solutions: Walkways as a mitigation solution? Thermal barriers over roof insulation? Other mitigation solutions?
Outline Project Background Fire Incidents Fire Testing of Roofs and PV Modules Proposed Test Plan Mitigation Solutions to be Tested
Test Plan General parameters: Test array Ignition source Air flow Roof assemblies to be tested. Mitigation solutions to be tested.
Test Array 4 x 5 test array 1 x 5 and 4 x 1 target arrays Standoff height ~5
Test Array Three module orientations: Flat All facing same direction East-west tented Images from https://www.solarcity.com/sites/default/files/zep-commercial-solutions-sheet-140914.pdf, http://blog.solarcity.com/topic/installation, and Grant, C. Fire Fighter Safety and Emergency Response for Solar Power Systems, Fire Protection Research Foundation Report, October 2013, p. 16.
Ignition Source Options considered: Gas burner Class A burning brand Standard ignitors (plastic bag, gauze, flammable liquid) Light combustibles Decided to use a 4-foot long gas burner: Reliable and repeatable Easily set and controlled
Air Flow Air flow will be provided by a bank of fans. Velocity will be 12 mph (5.3 m/s). Air speed will be checked with a velocity probe at the leading edge of the array.
Roof Assemblies Test roofs are typical of common roof assemblies: Membrane Thermoplastic olefin (TPO) Ethylene propylene diene monomer (EPDM) Polyvinyl chloride (PVC) Polyisocyanurate insulation Steel deck Roof assembly will measure 40 feet by 30 feet Image from http://www.tanenbaumroofing.com/tpo-single-ply-roofing/
Test Geometry
Outline Project Background Fire Incidents Fire Testing of Roofs and PV Modules Proposed Test Plan Mitigation Solutions to be Tested
Mitigation Solutions to be Tested Primary Walkways (with and without cover) Vertical barriers Non-combustible cover board on top of insulation Other possible solutions Gravel ballast on membrane Non-combustible PV module backing layer Increased standoff height
Test Matrix Test # Membrane Type Orientation Mitigation Solution 1 EPDM Flat None (baseline) 2 TPO Flat None (baseline) 3 PVC Flat None (baseline) 4 Worst case from 1-3 Angled None (baseline) 5 Worst case from 1-3 Tented None (baseline) 6 Worst case from 1-3 Worst case from 1-5 Walkway Cover 7 Worst case from 1-3 Worst case from 1-5 NC cover board 8 Worst case from 1-3 Worst case from 1-5 Vertical barriers 9+ Worst case from 1-3 Worst case from 1-5 TBD
Baseline Test Geometry
Test 6 Effect of Walkway Cover Walkways covered with paver blocks
Test 7 Non-Combustible Cover Board NC cover board under membrane across entire roof
Test 8 Vertical Barriers
Test 9+ - Potential Further Testing Repeat primary solution tests? Gravel ballast? Non-combustible backing layer? Increased standoff height?
Next Steps Finalize test plan Testing will be conducted in a later phase of the project
Thank You
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